Q.Mention the uses of surfactants.

Pulmonary surfactant is a phospholipid-rich fluid secreted into the alveoli that lowers surface tension, preventing the tiny alveolar sacs from collapsing and easing the work of breathing.

The alveoli (tiny air sacs in the lungs where gas exchange occurs) are lined internally by a thin film of fluid. Because this fluid–air interface naturally has surface tension (water molecules attracting each other), the alveolar walls would tend to stick together and collapse, especially in the smaller alveoli and during exhalation, making the lungs very difficult to re-inflate.

Specialized Type II alveolar cells secrete a substance called surfactant — a mixture of phospholipids and proteins — into this fluid lining. Surfactant spreads over the fluid surface and disrupts the cohesive forces between water molecules, thereby lowering the surface tension. This:

• Prevents alveolar collapse (atelectasis), especially at the end of expiration. …